In recent years, head-up displays (HUDs) reflecting images on windshields or the like to display information into drivers' field of view have been prevalent. The HUD reproduces a virtual image at a location approximately 4 m ahead of the windshield, enables the driver to confirm route guidance, emergency information, and the like without largely changing the line of sight, and contributes to safety.
In general, the HUD comprises a liquid crystal panel and an illumination device called a backlight which applies light to the liquid crystal panel. An image formed on the liquid crystal panel is transmitted by the light of the backlight and projected to the windshield. The image is reflected on the windshield, and a virtual image is thereby formed.
In the HUD, the backlight comprises a light source and a reflector which reflects a part or all parts of the light beam emitted from the light source to the liquid crystal panel. Increasing the directivity of the light emitted from the reflector in the backlight is a measure effective for increase in the brightness, reduction in the power consumption, and reduction in the heat generation. This directivity increases as the reflector becomes higher (i.e., as the distance of passage of light becomes longer). If the reflective surface of the reflector has a low reflectance, however, the light is lost and the brightness of the backlight becomes lower as the light is reflected on the reflective surface.